Copper physical vapor deposition targets and methods of making copper physical vapor deposition targets

ABSTRACT

The invention includes physical vapor deposition targets formed of copper material and having an average grain size of less than 50 microns and an absence of course-grain areas throughout the target. The invention encompasses a physical vapor deposition target, of a copper material and having an average grain size of less than 50 microns with a grain size standard deviation of fess than 5% (1−σ) throughout the target. The copper material is selected from copper alloys and high-purity copper material containing greater than or equal to 99.9999% copper, by weight. The invention includes methods of forming copper physical vapor deposition targets. An as-cast copper material is subjected to a multistage processing. Each stage of the multistage processing includes a heating event, a hot-forging event, and a water quenching event. After the multistage processing the copper material is roiled to produce a target blank.

TECHNICAL FIELD

The invention pertains to physical vapor deposition targets and methodsof forming copper physical vapor deposition targets.

BACKGROUND OF THE INVENTION

Physical vapor deposition (PVD) methods are used extensively for formingthin metal films over a variety of substrates, including but not limitedto, semiconductive substrates during semiconductor fabrication. Adiagrammatic view of a portion of an exemplary PVD apparatus 10 is shownin FIG. 1. Apparatus 10 includes a target assembly 12. The targetassembly illustrated includes a backing plate 14 interfacing a PVD or“sputtering” target 16. Alternative assembly configurations (not shown)have an integral backing plate and target. Such targets can be referredto as ‘monolithic’ targets, where the term monolithic indicates beingmachined or fabricated from a single piece of material and withoutcombination with an independently formed backing plate.

Typically, apparatus 10 will include a substrate holder 18 forsupporting a substrate during a deposition event. A substrate 20, suchas a semiconductive material wafer, is provided to be spaced from target16. A surface 17 of target 16 can be referred to as a sputteringsurface. In operation, sputtered material 24 is displaced from surface17 of the target and deposits onto surfaces within the sputteringchamber including the substrate, resulting in formation of a thin film22.

Sputtering utilizing system 10 is most commonly achieved with a vacuumchamber by, for example, DC magnetron sputtering or radio frequency (RF)sputtering.

Various materials including metals and alloys can be deposited usingphysical vapor deposition. Copper materials including high-purity copperand copper alloys are utilized extensively for forming a variety of thinfilm and structures during semiconductor fabrications. Sputteringtargets are typically made of high-purity materials since the purity ofmaterials can affect the deposited film with even minuteparticle-inclusions such as oxides or other non-metallic impurities canlead to defective or imperfect devices. For purposes of the presentdescription the term ‘high-purity’ refers to the metafile purity interms of the amount or percent by weight of a metal material (excludinggases) which consists, of a particular metal or alloy. For example, a99.9999% pure copper material refers to a metal material where 99.9999%of the total non-gas content by weight is copper atoms.

In addition to material purity, factors such as the grain size of atarget material and the grain size uniformity of the material can alsoaffect the quality of a resulting thin film produced utilizing theparticular target. In general, a relatively small grain size isdesirable for PVD targets to produce high quality thin films. However,it has recently been shown that conventional methodology for producinghigh-purity copper and copper alloy targets results in anomalous areasof coarse grains in the final target. It is desirable to develop targetshaving improved grain size uniformity and methodology for producingtargets with improved grain size uniformity.

SUMMARY OF THE INVENTION

In one aspect the invention encompasses physical vapor depositiontargets. The targets are formed of copper material and have an averagegrain size of less than 50 microns. The targets additionally have anabsence of course-grain areas throughout the target.

In one aspect the invention encompasses a physical vapor depositiontarget of a copper material and having an average grain size of lessthan 50 microns with a grain size non-uniformity (standard deviation) ofless than 5% (1−σ) throughout the target. The copper material isselected from the group consisting of high-purity copper materialcontaining greater than or equal to 99.999% copper, by weight, andcopper alloys.

In one aspect the invention encompasses methods of forming copperphysical vapor deposition targets. The methods include providing anas-cast copper material and performing a multistage processing of theas-cast material. Each stage of the multistage processing includes aheating event, a hot-forging event, and a water quenching event. Afterthe multistage processing the copper material is rolled to produce atarget blank.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Patent and Trademark Officeupon request and payment of the necessary fee.

FIG. 1 is a diagrammatic view of a portion of an exemplary physicalvapor deposition apparatus.

FIG. 2 is a flowchart diagram outlining methodology in accordance withone aspect of the invention.

FIG. 3 shows a comparison of grain structures of target blanks producedutilizing conventional methodology (Panel A) and methodology inaccordance with the invention (Panel B).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws “to promote the progressof science and useful arts” (Article 1, Section 8).

In general the invention involves production of physical vapordeposition targets having improved grain size uniformity such that areasof course grains are significantly reduced or eliminated relative totargets produced utilizing conventional methodology. Specifically, theinvention was developed for production of high-purity copper targets andhigh-purity copper alloy targets where the term “high-purity” typicallyrefers to a base metallic purity of greater than or equal to 99.99%.Where the material is an alloy, the term “high purity” refers to thepurity of the base copper to which one or more alloying elements havebeen added. Although described primarily with respect to copper andcopper alloy targets it is to be understood that methodology of theinvention can be adapted for production of targets of alternative metalor alloy materials.

Targets in accordance with the invention can be produced to have atarget size and shape configuration appropriate for utilization inconventional or yet to be developed PVD deposition systems. Targets ofthe invention can be constructed for utilization with a backing plate inconfigurations such as that illustrated in FIG. 1. Alternatively,targets of the invention can be monolithic targets which can be utilizedin an absence of an independently formed backing plate.

Copper targets in accordance with the invention can comprise high-puritycopper or high-purity capper alloy, can consist essentially ofhigh-purity copper or high-purity copper alloy, or can consist ofhigh-purity copper or high-purity copper alloy. Where the coppermaterial comprises a copper alloy, a material can preferably comprisecopper and at least one element selected from the group consisting ofAg, Al, In, Mg, Sn, and Ti. Preferred copper alloys can contain lessthan or equal to about 10% of total alloying elements, by weight.

Sputtering of high-purity copper and copper alloy targets formed byconventional methodology has revealed the presence of course grainregions with such regions having large grains of about 100-200 micronsor greater. The presence of such grains has been determined to affectthe quality and uniformity of thin films produced utilizing suchtargets. In contrast, copper targets and copper alloy targets inaccordance with the invention have reduced numbers and areas of coursegrains regions, and in particular instances methodology in accordancewith the invention entirely eliminates course grains throughout thetarget.

Methodology in accordance with the invention is described generally withreference to FIG. 2. A general process 100 includes providing a coppermaterial in an initial step 112. Typically, the copper material will bean as-cast billet either of a high-purity copper or of copper alloy. Thecopper material is subsequently subjected to a thermomechanicalprocessing 114. In contrast to conventional methodology,thermomechanical processing in accordance with the invention can utilizemulti-stage processing where each stage includes a heating event,followed by a forging event and subsequent quenching. The multi-stageprocessing will include at least two stages or “rounds” of heating,forging and quenching and can comprise three or greater than threestages.

During the multi-stage processing the temperature during the heatingevent is not limited to a particular value and can vary depending uponthe specific material being processed. Further, an initial stage of themulti-stage processing can utilize a heating event that is conducted ata first temperature while a second stage heating event is conducted at asecond temperature which varies relative to the first temperature.Typically, each heating event in the multi-stage processing is conductedat a temperature of greater than about 900° F. In particular instances,high-purity copper and particular copper alloys will be heated at 1050°F. for at least 30 minutes during each heating event, and in someinstances may be heated for at least 60 minutes. It is to be understoodthat the heating time will vary depending upon the particular heatingtemperature.

During the multi-stage processing, forging events can utilize hot upsetforging. Typically a forging event conducted in a first stage ofmulti-stage processing will produce a forged block having a first height(block thickness) and a subsequent forging event conducted in asubsequent stage of the multi-stage processing will produce a forgedblock having a second reduced height. After each forging event theforged block is preferably quenched into cold water. Such quenching ispreferably conducted for at least 8 minutes with specific time beingdetermined by the material mass and block thickness.

Multi-stage processing ultimately results in a final forged block whichis subsequently subjected to a rolling process 116. Rolling process 116preferably comprises cold rolling for further thickness reduction of theforged block. Rolling process 116 produces a roiled blank which istypically machined and cleaned to form a target blank.

The rolled blank can be subjected to additional processing comprising aheat treatment 118. Where the target is to be bonded to a backing plate,such as a CuCr backing plate, the heat treatment can be performed aspart of the target/backing plate bonding process. Typically, suchbonding is conducted utilizing hot isostatic pressing (HIPping). TheHipping will typically be conducted at a temperature of at least about480°. It is to be understood however, that the particular bendingtemperature during HIPping can vary depending upon the particularhigh-purity copper material or copper alloy material being bonded. Inspecific instances where a high-purity copper material or particularcopper alloys are utilized, the bonding will be performed utilizing atemperature of approximately 662° F. for about 2 hours. In accordancewith the invention, such bonding produces a diffusion bond having a bondstrength of greater than about 20 ksi.

After bonding, the target/backing plate assembly can be furtherprocessed by machining to form a finished copper or copper alloy targetassembly. The heat treatment performed as part of the bonding processresults in annealing or recrystallization of the copper material. Thecombination of the multi-stage processing and recrystallization resultsin fine grain size and uniform grain distribution with essentially nocourse grain areas, and in particular instances results in an absence ofcourse grain areas throughout an entirety of the target.

In an alternative embodiment where the rolled blank is to be utilized asa target in an absence of a backing plate, the rolled blank can besubjected to heat treatment 118 by annealing/recrystallizing at a heattreatment temperature as discussed above with respect to heat treatmentprocess 118. In general, the heat treatment will compriseannealing/recrystallizing at a temperature of at least about 480° F.,and in particular instances about 662° F. for about 2 hours. Afterannealing, the target blank is machined to produce a monolithic copperor copper alloy target for use without a backing plate. The heattreatment results in recrystallization. Due to the previous multi-stageprocessing, the recrystallization results in essentially no coursegrains and typically an entire elimination of course grains throughoutthe monolithic target.

Whether the target material is high-purify copper or copper alloy, andwhether a monolithic target or target assembly is formed, targetsproduced utilizing methodology as presented in FIG. 2, consistently haveaverage grain sizes of less than 50 microns with a standard deviation ofless than 10% (1−σ). In particular instances the standard deviation isless than 5% (1−σ).

Referring to FIG. 3, a comparison of target blanks produced byconventional methodology (Panel A) and methodology in accordance withthe invention (Panel B) is shown. The conventional target blank shown inPanel A has visible rough/shiny regions corresponding to course grainareas having grains of sizes exceeding 100-200 microns, in contrast, thetarget blank shown in Panel B produced in accordance with methodology ofthe invention has a notable absence of any such rough/shiny regions andin fact has an absence of course grain regions.

Processing of particular materials in accordance with the invention isfurther described in the examples below. It is to be understood that theexamples are not intended to limit the invention to any particularmaterial compositions, processing temperatures or conditions and are setforth to illustrate the effectiveness of the inventive processing.

EXAMPLE 1

A 6 inch diameter by 10 inch high as-cast copper alloy billet was heatedat 1050°F. for 60 minutes. The billet was then subjected to hot forgingto a first block height of 6.0 inches. The block was quenched into coldwater for longer than 8 minutes. The quenched block was reheated at1050° F. for 30 minutes followed by hot forging to a resulting secondheight of 3.3 inches. The twice forged block was quenched into wafer forgreater than 8 minutes. The resulting forged block was then cold rolledto an ultimate thickness of 0.93 inches. The roiled blank was machinedand cleaned and was subsequently bonded to a CuCr backing plate by hotisostatic pressing at 662° F. for 2 hours. The resulting target/backingplate assembly was machined to a finished copper alloy target assembly.The final target had a uniform grain size distribution with a standarddeviation of less than 5% (1−σ) and an average grain size of less than50 microns.

EXAMPLE 2

A roiled copper alloy blank was prepared as described above inExample 1. The rolled alloy blank was annealed by heat treating at 662°F. for 2 hours. The resulting target blank was machined to produce amonolithic copper alloy target which had a resulting grain size averageless than 50 microns and a uniform grain size distribution having astandard deviation of less than 5% (1−σ) throughout the target.

EXAMPLE 3

A high-purity (99.9999% by weight) copper as-cast billet was subjectedto two rounds of heating, hot forging, and water quenching, followed bycold roiling as described in Example 1. The rolled copper blank wasmachined and cleaned and was bonded to a CuCr backing plate at 662° F.for 2 hours utilizing hot isostatic pressing. After bonding, theassembly was machined to form a finished copper target assembly. Theresulting bond strength was greater than 20 ksi. The target had anaverage grain size of less than 50 microns and a grain size distributionstandard deviation of less than 5% (1−σ).

EXAMPLE 4

A roiled high-purity copper blank was produced as described in Example3. The blank was subjected to annealing by heating at 662° F. for 2hours. The target blank was subsequently machined to produce amonolithic target. The monolithic target had an average grain size ofless than 50 microns and a grain size distribution uniformity of lessthan 5% (1−σ).

For each of the four targets produced above in the examples the targethad an absence of course grain regions throughout the entirety of thetarget. The results of studies of grain sizes for targets of theinvention as compared to conventional targets is presented in Table I.Resulting grain sizes for a copper-aluminum alloy target produced inaccordance with the invention is presented in Rows 3 and 4 of the table,as compared to a target of identical composition prepared utilizingconventional processing (Rows 1 and 2).

TABLE I Grain size (microns) comparison at indicted target locations forconventional targets and targets of the invention. Edge Middle radiusCenter Average μm μm μm μm Top of conventional 27 80 64 57 target Bottomof 32 29 43 35 conventional target Top of target of the 32 29 32 31invention Bottom of target of the 32 29 32 31 invention

Additional grain size determinations were performed for multi-stageprocessed targets of the invention. The results for four independentlyformed copper-aluminum alloy targets are presented in Table 2. Grainsize determinations were performed at multiple target levels (surface,0.3 inch thickness and 0.6 inch thickness), with 9 samples being studiedper level. The standard deviation per level and for each target overallare specified.

TABLE 2 Grain size (microns) uniformity for multi-stage processedtargets. Plane Overall std dev std dev Target 1 2 3 4 5 6 7 8 9 Ave (1σ)(1σ) 1 0.0″ 29 29 32 29 32 32 35 32 29 31 2.1 4.1 0.3″ 29 32 32 35 29 2929 29 32 31 2.2 0.6″ 29 29 32 29 37 48 32 35 37 34 6.1 2 0.0″ 32 32 3232 48 37 32 32 35 35 5.3 4.0 0.3″ 32 27 32 32 32 29 29 29 32 30 1.9 0.6″29 29 32 32 27 29 29 35 35 31 2.9 3 0.0″ 35 29 35 35 32 32 32 48 32 345.5 4.5 0.3″ 27 32 29 32 29 29 29 32 29 30 1.8 0.6″ 32 29 29 32 29 35 4335 32 33 4.5 4 0.0″ 32 32 48 29 32 35 37 35 37 35 5.5 4.4 0.3″ 29 27 2929 29 29 32 29 32 29 1.6 0.6″ 29 27 32 29 37 37 32 32 32 32 3.4

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

1-9. (canceled)
 10. A method of forming a copper physical vapordeposition target comprising: providing an as-cast copper material;performing a multi-stage processing of the as-cast material, each stagecomprising a heating event, a hot forging event and a water-quenchingevent; and after the multi-stage processing, rolling the copper materialto produce a target blank.
 11. The method of claim 10 further comprisingannealing the target blank.
 12. The method of claim 11 wherein theannealing is conducted at a temperature of at least about 480° F. 13.The method of claim 10 further comprising hot isostatic pressing theblank to a backing plate to produce a diffusion bond having a bondstrength of greater than or equal to 20 ksi.
 14. The method of claim 13wherein the isostatic pressing is conducted at a temperature of about662° F. for about 2 hours.
 15. The method of claim 10 further comprisingmachining the target blank to produce a monolithic target.
 16. Themethod of claim 10 wherein the copper material is high-purity copperhaving a purity of greater than or equal to 99.9999% copper, by weight.17. The method of claim 10 wherein the copper material is a copperalloy.
 18. The method of claim 17 wherein the copper alloy comprisescopper and one or more elements selected from the group consisting ofAg, Al, In, Mg, Sn, and Ti.
 19. The method of claim 10 wherein themulti-stage process comprises a first stage comprising a first heatingevent wherein the copper material is heated at a temperature of greaterthan or equal to 900° F., and a second stage comprising a second heatingevent wherein the copper material is heated at a temperature of greaterthan or equal to 900° F. for at least 30 minutes.
 20. A copper physicalvapor deposition target framed by the method of claim 10.